The present invention relates to the field of construction machines comprising caterpillar chain drives (chain drives), for example road finishing machines or road milling machines, in particular to a device and to a method for measuring a distance or travel distance in a construction machine having a caterpillar chain drive, and to a construction machine having such a device.
Different approaches for measuring a distance covered by a construction machine are known. EP 0 388 819 A1, for example, discloses a path measuring means for a road finishing machine having a mounting plank, the path measuring means comprising a measuring wheel running along within the operating width of the mounting plank. Such a measuring wheel is of disadvantage since an additional moving element has to be provided in the construction machine, wherein the element gets dirty by the material processed, in particular when being used in a road finishing machine and, consequently, no longer runs along smoothly, the result being a corruption of the distance measured.
EP 1 557 493 A2 describes a method for operating a road finishing machine, wherein a position of the road finishing machine is determined via a navigation system either at the beginning or the end of an installing process or continuously. A real distance installed is determined from the positions and indicated while considering the course of the path, for example road bends or gradients. Of disadvantage with this method is the fact that measuring the distance covered is based solely on a satellite-supported navigation system, for example the GPS system and consequently is prone to errors in practice. Due to weather and environmental influences, a reliable GPS signal cannot always be ensured, for example when the road finishing machine passes below bridges or in tunnels, so that determining the position of the road finishing machine and, thus, establishing the distance covered and the actual distance installed is imprecise. Furthermore, it is of disadvantage that a course of the road to be installed needs to be known beforehand, since otherwise the distance cannot be calculated precisely.
WO 2012/168186 A1 describes a method for determining an area milled by a construction machine or a breakdown machine having a milling roll. The position of the machine is determined continuously by means of position determining means and a GNSS (global navigation satellite system) receiver or by means of a total station and a prism arranged on the machine. Subareas are calculated together with the width of the milling roll and summed up to form an overall area. Overlapping subareas, that is parts of areas processed several times, are subtracted again from this overall area so as to obtain an actually milled area. The information whether the milling drum is switched on or not, either has to be input manually by the operator or may be retrieved from the machine controller. With disturbances in receiving the GNSS signal, replacement data for missing or erroneous position data are calculated, which supplement or replace same. Thus, the replacement data are gained either from the past or further course of the distance or from the feed and steering angle data of the machine. Of disadvantage with this procedure is that the position determining means needs access to the machine parameters and/or needs to know the course of the distance covered by the machine so that, in the case of disturbances in receiving the GNSS signal, replacement data may be calculated. It is of further disadvantage that access to machine parameters is also necessitated for obtaining information as to whether the machine operates while moving or not, that is, for example, whether a milling drum is switched on or not. Alternatively, this information may also be input manually by an operator, which, however, is of disadvantage in that wrong calculations result when no information is input.
GB 2 255 640 A discloses a road finishing machine comprising a contactless approximation sensor arranged in the region of the front wheel and a spoke located in a detection region of the approximation sensor and arranged in the transverse direction of the road finishing machine behind the front wheel, the spoke being attached to the axis of the front wheel and turning uniformly with the front wheel when the road finishing machine moves. When the road finishing machine moves, due to the rotary movement of the spoke, impulses form at the approximation sensor, using which a distance covered by the road finishing machine may be measured. Furthermore, a switching element having a lever directed downwards and projecting into the material still to be processed is located in front of the spreading auger. Using this switching device, it may be determined whether the road finishing machine performs a forward movement or not and, resulting from this, a distance measurement is activated or deactivated. Of disadvantage with this system is the fact that, on the one hand, the switching device, in the region in front of the spreading auger, is a mechanical device and, consequently, prone to wear and, on the other hand, the sensor arranged in the region of the front wheel is of disadvantage since the sensor arrangement has to be installed behind the front wheel in a highly complicated manner and, thus, is difficult to access in the case of repair and may only be replaced while entailing big efforts. This results in a longer and inadvertent downtime of the road finishing machine. Additionally, due to its mounting position, the sensor arrangement is difficult to clean when dirty. Another disadvantage of this system is that, even with a defect in one of the two sensors or one of the two devices, that is either the switching device in front of the spreading auger or the sensor arrangement behind the front wheel, measuring or calculating the distance covered is no longer possible or will be erroneous until the defective device has been repaired.
Departing from this known technology, the object underlying the present invention is providing an improved approach for measuring and calculating a distance where the disadvantages of known implementations mentioned above are avoided and which allows easy, reliable and precise measurement and calculation of the distance.